1. Field of the Invention
The present invention relates to an N-vinylformamide (hereinafter referred to as "NVF") composition. More particularly, it relates to an NVF composition having excellent stability upon storage and a method of handling NVF.
2. Prior Art
NVF may be utilized as polymerizable monomeric materials. In particular, modified polymers derived therefrom have recently been expected to be applied as cationic polymers having a vinylamine unit to dehydrating flocculants for organic sludge and paper-making reagents.
It is known, however, that NVF may often be deteriorated partially resulting in decrease of its quality during its storage, purification by distillation or polymerization reaction. Such deteriorated NVF cannot provide high viscosity polymers in a stable manner.
Several means for preserving NVF stably have been known.
Japanese Patent Application Laying-open (KOKAI) No. 63-264559 (1988) proposed to store NVF under an inert gas environment in a sealed vessel. It is disclosed that the storage stability may be further improved by diluting NVF with water 5 times the weight of NVF and adjusting the pH to 6 to 8 with an aqueous alkaline solution. This proposed method is effective to some extent but insufficient to improve the storage stability of NVF.
Japanese Patent Application Laying-open (KOKAI) No. 62-195352 (1987) proposed to adjust the pH of NVF to near neutral upon purification by distillation thereof. It is recommended to add an inorganic acid, such as sulfuric or hydrochloric acid, or an organic acid, such as acetic or formic acid when the pH is high. In the proposed method, however, the resulting product may be contaminated with acidic substances although any basic substances should be eliminated. Further, the storage stabilizing effect is not consistently provided.
Japanese Patent Application Laying-open (KOKAI) No. 61-289068 (1986) describes that among conventional stabilizers for vinylic compounds, hydroquinone, phenothiazine or phenylenediamine is insufficient to stabilize NVF during its purification by distillation or storage, but only thioureas are effective. However, the storage stability is not fully satisfactory at ordinary temperatures although the stabilization effect is excellent upon distillation of NVF at higher temperatures.